Tips on making the Tracker Bar and Crankshaft
by Noel Maw
|Making the Tacker Bar
To overcome the difficulty of accurately spacing the holes in the tracker bar, I made a drilling jig out of 1/4" (8mm) plate. To do this I used a mill/drill which, if you haven't seen one, is a small machine tool where the work table moves horizontally relative to the drill head. This can be done with great accuracy using hand-wheels graduated in inches or millimetres. I drilled the first hole then indexed the work table across exactly the right amount for the next hole. I repeated this procedure for the twenty holes remembering that the spacing for the bass pipes is greater. I found that drilling a pilot hole with a lathe centre drill was necessary to prevent the 4mm (or 6mm) drill wandering. In use, the tracker bar blank is clamped between the jig and a piece of thickish wood so that, when the drill breaks through the back of the blank, it exits cleanly. The jig can be used again and again.
This, in my opinion (and for someone like me with poor eyesight), is by far the easiest way to achieve the accuracy needed. If you cannot lay hands on a mill/drill then may I suggest you trot along and join your nearest Model Engineering Society. You will find that they will welcome you and you will have access to all the practical help you will ever need. Model engineering and organ building have so much in common.
Another small change that I thought would be worthwhile was to use a 4 1/2mm punch for my music rather than the recommended 4mm. I argued that cumulative tolerances between the music roll and the tracker bar might cause a slight misalignment of the holes - if they are both sized exactly the same. So adding 1/2mm to the punched holes would help to overome this potential defect I thought. It certainly works, and seems to have no ill effects.
Still on tracker bars: I was in our local school stationers and I found that I can still buy boxwood school rulers. By chance these are exactly the right shape for the tracker bar top blank. All I needed to do was to sand off the graduations and figures and the job was ready to be drilled. The wood of these rulers is strong, dense and stable and you can make two tracker bars out of one ruler, cost 40 pence!
Making the Crankshaft (without
I increased the web thickness of the cranks to 1/4" (depth half inch) and the shafts to 5/16" diameter (or the metric equivalents). My sketch, I hope, makes things clear. The webs were drilled and reamed in pairs. There is no additional work here because you have to do that if you silver solder or weld. I assembled the crank to check that everything was OK then I dismantled it and gave the whole thing a thorough clean. I used my stock of carbon tetrachloride for this but you might not wish to use CTC because it is a bit nasty. I am told that isopropyl alcohol is just as good but I have no experience of it. Then I re-assembled the job using LoctiteType 601. Perhaps unnecessarily I left the job overnight to cure. Finally I drilled the webs where I show in the sketch, using a number 52 drill, and then I drove in 1/16" diameter roll pins. The finished crank retained its shape well and it looks nice and clean and polished. Again the local Model Engineering Club will take an interest in the job.
Steel stock, roll pins and Loctite can be bought from:
Good Luck! Noel Maw.
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